South Korea urged Japan on Tuesday to retract its repeated territorial claim over Dokdo, a pair of rocky outcroppings in the East Sea, saying it will only impede efforts to move forward bilateral ties.

It was a reminder of longstanding diplomatic rifts between the neighboring countries despite a call for firm unity among regional powers to handle Pyongyang's recent peace overtures.

In a statement, South Korea's foreign ministry denounced the description of sovereignty over Dokdo in Japan's yearly foreign policy document, known as the Diplomatic Bluebook, reported to the Cabinet earlier in the day.

The ministry lodged a strong complaint against the Japanese government's "unjustifiable" claim over the ownership of Dokdo, which is effectively controlled by Seoul.

"The Japanese government will have to recognize that reiterating the unjustifiable and preposterous assertion about Dokdo won't be of help at all to the establishment of forward-looking South Korea-Japan relations,' the Ministry of Foreign Affairs said.

It stressed that Japan's move will have no effect on South Korea's firm territorial sovereignty as clarified by history, geography and international law.

"The government will deal resolutely with any of Japan's provocations related to Dokdo," it said.

Koichi Mizushima, minister at the Japanese Embassy in Seoul, enters the South Korean foreign ministry's building on May 15, 2018. (Yonhap)Koichi Mizushima, minister at the Japanese Embassy in Seoul, enters the South Korean foreign ministry's building on May 15, 2018. (Yonhap)

The ministry summoned Koichi Mizushima, minister at the Japanese Embassy in Seoul, to lodge a formal protest. He refused to answer questions from reporters, entering the ministry building.

Kim Yong-kil, director general for the ministry's Northeast Asian affairs, told the minister that Seoul can't accept Tokyo's unilateral naming of the body of waters between the two nations, officials said.

In the diplomatic paper, Japan said the waters shouldn't be called the East Sea.

"In particular, (Kim) made clear that (the government) can't accept Japan's unjust claim regarding the East Sea name," the ministry's spokesman Noh Kyu-duk said at a press briefing. "(He) stressed that the East Sea is the correct name that has been used for more than 2,000 years in our country."

Japan's naming of the sea has become better known globally as a legacy of its colonial rule of Korea from 1910-45, South Korea points out.

As a realistic alternative, the government has long campaigned for the simultaneous use of the South Korean and Japanese names.

Noh Kyu-duk, spokesman for South Korea's foreign ministry, in a file photo (Yonhap)Noh Kyu-duk, spokesman for South Korea's foreign ministry, in a file photo (Yonhap)

Unlike the 2017 version, meanwhile, Japan left out the expression that South Korea is "the most important neighbor" to share strategic interests with Japan.

It represents an apparent departure from the Shinzo Abe administration's friendly gestures toward Seoul in dealing with the issue of Japanese nationals abducted by North Korea decades ago.

In talks with South Korean President Moon Jae-in, Abe requested Seoul's support for Tokyo's efforts to resolve the matter. (Yonhap Nees)